The role of coarse aggregates in hydrophobized hydraulic concrete

Concrete materials with decreased water-absorption characteristics are optimum for some construction applications. Hydrophobicity accompanied by decreased water absorption in a concrete material can be achieved through its formulation with hydrophobic silica particles. Despite this effect of hydrophobic additions to concrete, the water absorption and hydrophobicity of the final concrete materials can be affected by the water affinity of the coarse aggregates used in their preparation. The role of these coarse aggregates was studied in concrete with added hydrophobic silica particles and prepared with three coarse aggregates with marked differences in their water absorption: quartz rocks (low), igneous andesitic rocks (medium) and igneous basaltic rocks (high). The hydrophobicity and water-absorption characteristics of the concrete materials depended on the coarse aggregates used in their preparations. The materials prepared with quartz as coarse aggregates produced less water-absorbing materials. In contrast, the use of igneous basaltic rocks produced materials with greater absorption. A pretreatment involving impregnation of the igneous basaltic rocks with hydrophobic particles before their use in the preparation of concrete material caused significantly decreased water absorption.